Phase-contrast X-ray microtomography links Cretaceous seeds with Gnetales and Bennettitales

Abstract

Over the past 25 years the discovery and study of Cretaceous plant mesofossils has yielded diverse and exquisitely preserved fossil flowers that have revolutionized our knowledge of early angiosperms, but remains of other seed plants in the same mesofossil assemblages have so far received little attention. These fossils, typically only a few millimetres long, have often been charred in natural fires and preserve both three-dimensional morphology and cellular detail. Here we use phase-contrast-enhanced synchrotron-radiation X-ray tomographic microscopy to clarify the structure of small charcoalified gymnosperm seeds from the Early Cretaceous of Portugal and North America. The new information links these seeds to Gnetales (including Erdtmanithecales, a putatively closely related fossil group), and to Bennettitales--important extinct Mesozoic seed plants with cycad-like leaves and flower-like reproductive structures. The results suggest that the distinctive seed architecture of Gnetales, Erdtmanithecales and Bennettitales defines a clade containing these taxa. This has significant consequences for hypotheses of seed plant phylogeny by providing support for key elements of the controversial anthophyte hypothesis, which links angiosperms, Bennettitales and Gnetales.

Virtual taphonomy using synchrotron tomographic microscopy reveals cryptic features and internal structure of modern and fossil plants

“…Material SRXTM has proven to be an excellent imaging system, not only for fossil plants [as demonstrated for charcoalified reproductive structures (17,18,(22)(23)(24) and megaspores (25)], but also for modern plants, which we demonstrate here (Fig. 1).…”

“…Also, SRXTM has very high resolution, up to 0.35 m, and thus provides better resolution than HRCT. Combined with recent developments in phase contrast methods (17,20,21), synchrotron facilities are a powerful tool for noninvasive, volumetric investigation of a broad range of material.There are many actual and potential uses of SRXTM for studying both fossil and extant plants. Here, we evaluate the benefits of SRXTM, and explore potential applications and the predictive value of digital preparation to (i) provide high-quality anatomical detail in multiple planes of section from a single specimen, comparable to traditional histology, but avoiding associated technical problems; and (ii) introduce a technique-''virtual taphonomy''-including production of both 2D and 3D virtual potential fossils.…”

“…Also, SRXTM has very high resolution, up to 0.35 m, and thus provides better resolution than HRCT. Combined with recent developments in phase contrast methods (17,20,21), synchrotron facilities are a powerful tool for noninvasive, volumetric investigation of a broad range of material.…”

Ptilophyllum muelleri(Ettingsh.) comb. nov. from the Oligocene of Australia: Last of the Bennettitales?

“…However, recent cladistic analyses indicate that Cycadales and Bennettitales are not closely related, although controversy continues regarding the interpretation of certain reproductive characters and the phylogenetic position of the Bennettitales within the spermatophytes (Friis et al 2007;Rothwell et al 2009). Several analyses resolve Bennettitales as a sister group to the Gnetales and angiosperms within an ''anthophyte'' clade (Crane 1985;Nixon et al 1994;Donoghue and Doyle 2000;Hilton and Bateman 2006;Friis et al 2007). On this basis, their stratigraphic range and anatomical character states have become important in evaluating the cladogenesis of the flowering plants.…”

Enhanced x-ray imaging for a thin film cochlear implant with metal artefacts using phase retrieval tomography

“…19,20 This direct method has been applied also to image real samples. 21 Apart from the ability to image low density objects, phase retrieval tomography is also useful when imaging objects that exhibit almost uniform absorption properties but possesses a significant difference in phase shift properties. 22 While phase contrast and phase retrieval are used to deal with cases where there is not enough absorption, metal artefact reduction (MAR) is used to deal with the case where there is too much.…”